1. Field of the Invention
This invention relates generally to a molding composition for inhibiting plateout of pigment on the surface of a mold or shaping apparatus during the molding or shaping operation. The composition also exhibits high compatibility of its components and improved thermal and oxidation stability. The molding composition of the invention comprises a thermoplastic resin, a reagent containing a reactive functionality, a fluorescent pigment and a metal salt or complex.
2. State of the Art
The pigmenting of thermoplastic resins, which are used to prepare molded articles by various molding and shaping processes, is well known. However, there have been numerous problems associated with preparing such molded articles from pigmented thermoplastics. For example, pigments are generally chemical compounds of radically distinct structure and chemistry from that of the thermoplastic resin to which the pigment is added. Therefore, the pigment is often times incompatible with the thermoplastic resin and this, in turn, creates problems of non-uniform dispersability within the thermoplastic resin molding composition as well as resulting in the pigment rising to the surface of the thermoplastic resin during the molding or shaping process. If the pigment does rise to the surface, it may adhere to the wall of the mold during the formation of the particular article. This phenomenon is referred to as "plateout". If this occurs, the resultant molded article will not have the desired uniformity and pigmentation. Also, with continuous use of the mold, the pigment will build up on the surface of the mold which, in turn, requires down-time of the molding apparatus in order to clean the mold surface.
Many of the problems associated with pigmenting thermoplastic resins for use in the preparation of molded articles have been satisfactorily resolved. For example, In U.S. Pat. No. 3,462,388 fluorescent compound bonded polymers, which can be molded or spun into filaments, are disclosed. It is disclosed in the patent that the fluorescent compounds are chemically bonded to the polymer to produce the desired properties.
U.S. Pat. No. 3,592,777 discloses a polymer blend that exhibits fluorescence when subjected to a selected activation energy. The polymers are prepared from an aliphatic or aromatic substituted aliphatic diketone and an aliphatic diamine which results in a linear non-cross-conjugated polymer.
U.S. Pat. No. 4,331,584 discloses various styryl compounds for coloring of synthetic resins. It is disclosed that these pigments have improved fastness to sublimation and increase pH sensitivity.
In U.S. Pat. No. 4,238,384, a method for incorporating additives in polymer materials is disclosed. The additives include stabilizers, anti-oxidants and antistatic agents. An optical brightener is incorporated in the thermoplastic polymer, and subjected to radiation to determine the degree of uniformity of the distribution of the additive-brightener blend.
U.S. Pat. No. 4,626,565 discloses a process for the preparation of polypropylene-based resin compositions. The composition is suitable for use in the preparation of such molded articles as automobile bumpers, fenders, body side members and the like. The polymers exhibit excellent low temperature impact resistance, high molding fluidity, good paintability and high stiffness.
U.S. Pat. No. 3,545,676 discloses blends of ionomer resins and elastomer. These blends give molded articles having both resilience and toughness.
U.S. Pat. No. 4,223,113 discloses polyester molding compositions which crystallize rapidly and thus allow lower mold temperatures along with shorter injection cycles.
U.S. Pat. No. 3,915,884 discloses various modified polyamides which are useful matrix materials for incorporating dyes, particularly fluorescent dyes. The dye incorporated into the modified polyamide forms a pigment having high heat stability.
U.S. Pat. No. 2,938,873 discloses various fluorescent pigments useful for pigmenting thermoplastic resins. The pigments exhibit improved light fastness and color brightness.
U.S. Pat. No. 3,303,168 discloses thermoplastic resins and molded articles thereof which are pigmented with fluorescent pigments.
None of the above-discussed patents disclose techniques relating to or solutions for the plateout problem. Furthermore, none of these patents disclose the unique composition of the present invention